The present invention is directed to a writing head for an ink printing device comprising piezo-electric drive elements having a shape which changes due to suitable polarized drive pulses and under whose influence ink is sucked out of an ink reservoir through a common ink feed channel during an expansion phase and a small volume of ink is ejected in the form of an ink droplet during a following contraction phase.
The essential functioning principle of an ink printing device is based on the fact that a drop-by-drop ink ejection from an ejection nozzle occurs under the influence of a transducer element, preferably a piezo-electric transducer drive element. As known, piezo-electric drive elements, ink channels with the discharge openings, and the feeds for the ink from a supply system are combined in so-called writing heads. In a known writing head, the drive elements have the form of a small piezo-electric tube, which embraces or surrounds the ink channel over part of its length. Given suitable drive of the small piezo-electric tube, the geometric dimensions thereof are changed and a pressure or shock wave is produced on the inside of the ink channel. This shock wave will cause a small drop of ink to be ejected from the discharge opening of the ink channel and it is noted that this discharge opening lies opposite the recording medium. The individual drive of the multitude of such drive elements disposed in a writing head creates the possibility of representing characters constructed matrix-like in an arbitrary shape.
Writing heads constructed in such a fashion have proven themselves very well in practice. There are problems, however, which occur in view of the manufacture of such writing heads. These problems essentially consist in the fact that the individual ink channels and the small piezo-electric tubes surrounding them must respectively be very exactly assembled, adjusted and cast out or encapsulated. The cost for manufacturing connected with these steps is considerable. It even increases when the spacing at the end of the writing head lying opposite a recording medium must be made very narrow in order, for example, to increase the number of discharge openings. Since according to the prior art, the ink channels are respectively terminated by a nozzle plate whose openings have a smaller diameter than the diameter of the ink channel, a limit is encountered for technological reasons.
In order, among other things, to reduce these problems, it has been disclosed to employ a so-called piezo-comb as a drive element. In this case, the drive element is composed of piezo-ceramic material shaped comb-like whose teeth are respectively disposed in front of the discharge opening. When driven, the teeth of the piezo-comb act like a flexure resonator so that they move quickly in a direction toward the discharge opening allocated to them and thus effect an ejection of a droplet. The problem connected with the writing head constructed in such a fashion essentially in that special measures for attenuating and limiting the cross-talk influences must be provided. These have a disturbing effect particularly during operation of such a writing head.